It is now widely accepted that the TGF-beta signaling pathways can both suppress tumor formation and promote tumor progression and that both effects are mediated largely through tumor cell autonomous TGF-beta signaling. Data generated during this grant period with conditional knockout of TGF-beta signaling in epithelia support the hypothesis that epithelial cell autonomous TGF-beta signaling is tumor suppressive and demonstrate that metastases can not only occur but are enhanced with knockout of the type II TGF-beta receptor (Tgfbr2) in mammary carcinoma cells. However, systemic inhibition of TGF-beta signaling markedly suppressed pulmonary metastases in the MMTV-c-neu/DNIIR mice. This indicates that the effect of systemic inhibitors of TGF-beta in suppressing metastasis is largely on host cells. These results have modified our hypotheses concerning the mechanism of TGF-beta promotion of tumor progression. We now propose that tumor cell autonomous signaling by TGF-beta can suppress rather than enhancing metastases, and that TGF-beta signaling in host cells is a significant component of both the tumor suppressive and the tumor promotion effects of TGF-beta in vivo. We will test these hypotheses through the following specific aims by determining the changes in the carcinoma cells and their microenvironment associated with knockout of the type II TGF-beta receptor gene, Tgfbr2, in tumor cells that lead to increased metastases. Specific Aim 1. Determine the effects of systemic inhibition of TGF-beta signaling on mammary tumor formation and metastases from MMTV-c-neu and MMTV-PyVmT-induced mammary tumors in the context Tgfbr2 knockout in mammary epithelial cells effected by both MMTV-Cre and WAP-Cre. Specific Aim 2. Determine the influence of timing of loss of TGF-beta signaling during mammary tumor formation and progression on metastatic spread using inducible MMTV-Cre. Specific Aim 3. Determine mechanisms for enhanced metastatic capability with loss of tumor cell TGF-beta signaling by examining both tumor cells and their microenvironment.